It is well known that bark and small limbs can be removed from logs in a debarking device by passing the log between a set of rapidly rotating, upper and lower debarking drums in the debarking device, each of which have a plurality of debarking chains, also called flail chains. The debarking chains repetitively strike the surface of the log with significant force at a high rate of speed, effectively tearing away any small limbs and virtually all of the bark on the log in preparation for a chipping operation in which the log is chipped into small pieces appropriate for further processing into wood pulp for paper manufacturing or the manufacturing of composite products such as chip board, oriented strand board and engineered lumber.
Logs are conveyed lengthwise through the debarking device along a predetermined feed plane. The upper drum is located above the feed plane and the lower drum is located below the feed plane, each at a distance from the feed plane to allow the debarking chains, or flail chains, together to clear bark and limbs from the entire surface of the log. It will be appreciated that each set of debarking chains, associated with respective debarking drums, must reach at least the midpoint of the sides of the log. Some debarking devices have additional debarking drums some of which are fix drums and some of which are often “floating” drums.
It will be appreciated that in prior designs, the debarking chains consist of elongated or oblong chain links that have projected wear life based primarily upon stress applied to the unshaped end portion of the respective chain links as these links repetitively strike the outer surface of the logs and as these links strike each other when the links recoil following such impacts. This projected wear life dictates frequency of debarking chain replacement. It will be appreciated that any extension of the projected wear life of a set of debarking chains will reduce cost for debarking operations in that extended use will reduce the number of chains used per unit of logs debarked or wood chips generated.
In normal use, a set of debarking chains are generally attached to a debarking drum, used for a predetermined amount of time or until any links are worn to a predetermined amount of wear near the point of breakage based on periodic inspection of the debarking chain, and then disconnected, flipped end to end, before being reattached and used again for another set amount of time or predetermined amount of wear.
Debarking is important in chipping operations, because this processing step minimizes the residual amount of bark mixed into wood chips from subsequent chipping operations. Wood chips are less desirable for pulping operations when they contain bark that is not removed from logs before the logs are chipped.
A greater fear in these operations, however, is that the debarking chains will break and damage the chipper. This is one of the key reasons that operators carefully avoid extending the use of a set of debarking chains beyond the projected wear life for the chains. If any of the chains break and any of the metal links get into the chipper, which is generally rotating at a very high rate of speed, any consequent damage to the chipper can result in added operating costs due to machine downtime and needed replacement parts. Additionally, there exists the risk that breaking links may cause link debris to enter adjacent machinery, causing further damage and downtime.
For these and other reasons, it will be appreciated that there is a practical need to increase the projected debarking chain wear life, thereby reducing chain replacement cost per unit of processed wood products, along with associated costs of replacement materials and machine downtime.
The present invention provides improvements which address these and other limitations associated with the prior art.